Wraith uses a headless browser to create screenshots of webpages on different environments (or at different moments in time) and then creates a diff of the two images; the affected areas are highlighted in blue.

You can configure it in various ways but in a nutshell you provide it with two URLs, and it will take screenshots of both and compare them, providing you with a visual diff of the two as well as a 'score' percentage of the differences (if any).

Installation

Setup is easy.

You will need ImageMagick installed, as well as a headless browser like PhantomJS.

Then simply:

gem install wraith

If you run 'wraith' without any options it will print out some useful help: